Menstrual cycle

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Cyclical, approximately monthly vaginal bleeding in women of reproductive age caused by shedding of the endometrium in the absence of implantation of a embryo.

The menstrual period occurs about 14 days after ovulation, unless pregnancy occurs. Ovulation is somewhat variable and unpredictable. Women whose periods are infrequent cannot count on being infertile.


  1. Spiral arteries contract for 4-24 hours
  2. Spiral arteries dilates
  3. blood lakes form, haemorrhage into endometrium
  4. fibrin plugs, platelet aggregation
  5. spiral arteries constrict
  6. epithelium shed
  7. re-epithelisation (under oestrogen control)

Disorders of menstruation

uterine bleeding, excessive in amount and/or duration of flow occurring at regular intervals
painful periods
infrequent, irregular episodes of bleeding usually occurring at intervals of more than 40 days
frequent but regular episodes of uterine bleeding, usually occurring at intervals of less than 21 days
uterine bleeding, usually not excessive but occurring at irregular intervals
uterine bleeding, usually excessive and prolonged occurring at frequent irregular intervals
uterine bleeding, regular but decreased in amount
Intermenstrual bleeding
uterine bleeding, usually not excessive occurring between otherwise regular uterine cycles

See also

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